The present invention relates to a display system for displaying graphs such as an information processing unit, and more particularly to a method of displaying a thick line.
As a method for displaying a thick line, a technique has been generally known which generates and displays a thick line by drawing a line by a parallel movement of a reference line component in the X direction or in the Y direction, as discussed in the Japanese Patent Unexamined Publication No. JP-A-61-240381.
However, no particular consideration has been given to a clipping processing for processing a display range by two or more clip frames in the case of a multi-window environment and the like. Therefore, there arises a problem that when a clipping processing is necessary, if a parallel-moved line component is added to a reference line component after a clipping processing, a portion of a clipped end is not displayed.
This problem will be explained in detail by taking an example of a multi-window environment, with reference to FIG. 5.
In the drawing, 6 designates a monitoring screen, 91 and 92 designate windows of a multi-window, and 93 also designates a window.
In a multi-window environment, it is general that when a window is not square, a square window or a clip-framed display is carried out in order to avoid complex processing or in order to increase a processing speed.
In other words, a thick line 10 is displayed by dividing it by the clip frames 91 and 92.
Consider a case that the thick line is clipping processed by using the clip frame 91 to make a display. First, a reference line component 100 of the thick line 10 is clipped by the clip frame 91, and coordinates of start and end portions of additional line components 101 to 104 are obtained.
Then, the reference line component and the additional line components are drawn, and, then, the thick line of the portion of the clip frame 91 is displayed. In this case, the additional line component 101 and the additional line component 102 which are positioned above the reference line component 100 do not reach the clip frame 91, and some portions are not displayed. The additional line component 103 and the additional line component 104 which are positioned below the reference line component 100 exceed the clip frame 91. Therefore, they are displayed by the clipping processing.
In the case of the clip frame 92, display processing is also carried out in the similar manner. When display is carried out in the manner as described above, there occur missing portions at the border of the clip frame where one thick line should be intrinsically displayed.
As a prior art for preventing this phenomenon, a technique is known according to which coordinates of start and end points of additional lines are obtained in addition to start and end points of a reference line component before a clipping processing, then the additional line components and the reference line component are drawn and these line components are clipping processed, as described in the Japanese Patent Unexamined Publication No. JP-A-63-225882.
When coordinates of the start and end points of the additional line components are obtained in addition to the start and end points of the reference line components before the clip processing, then coordinates of the reference line components and the additional line components on the clip frame are obtained and the additional line components and the reference line component are drawn, there occurs a problem of dropouts between the adjacent lines as discribed in the Japanese Patent Unexamined Publication No. JP-A-63-225882.